Systems and methods for determining the quantity of a combustion product in a vehicle exhaust

ABSTRACT

Exhaust after treatment systems for internal combustion engine powered vehicles are provided. One system includes logic in the form of one or more routines implemented by one or more of the system&#39;s components for determining the quantity of NO 2  present in the exhaust that exits an oxidation catalyst, such as a diesel oxidation catalyst (DOC), without the use of an NO 2  sensor. Results from such a determination may then be used to estimate the amount of soot present in the particulate filter. This estimated value of soot present in the particulate filter can then be subsequently used to determine when the particulate filter should be actively regenerated.

BACKGROUND

Internal combustion engine exhaust emissions, and especially dieselengine exhaust emissions, have recently come under scrutiny with theadvent of stricter regulations, both in the U.S. and abroad. Whilediesel engines are known to be more economical to run than spark-ignitedengines, diesel engines inherently suffer disadvantages in the area ofemissions. For example, in a diesel engine, fuel is injected during thecompression stroke, as opposed to during the intake stroke in aspark-ignited engine. As a result, a diesel engine has less time tothoroughly mix the air and fuel before ignition occurs. The consequenceis that diesel engine exhaust contains incompletely burned fuel known asparticulate matter, or “soot”. In addition to particulate matter,internal combustion engines including diesel engines produce a number ofcombustion products including hydrocarbons (“HC”), carbon monoxide(“CO”), oxides of nitrogen (“NOx”), and oxides of sulfur (“SOx”).

After treatment systems may be utilized to reduce or eliminate emissionsof these and other combustion products. For example, diesel particulatefilters, such as catalyzed soot filters and others, can be used to trapdiesel particulate matter and reduce emissions. The collection, orloading, of soot leads to an increase in exhaust pressure, which maydegrade engine performance. To remove the particulate matter, theparticulate filter can be passively regenerated by the presence of NO₂in the exhaust. Additionally, particulate filters may undergo activeregeneration to eliminate trapped diesel particulate matter by addingexternal energy into the exhaust stream, thereby raising the temperatureof the particulate filter up to approximately 400 degrees Celsius with afuel-borne catalyst and up to 600 degrees Celsius without a fuel-bornecatalyst.

However, excessive regeneration of the particulate filter consumesadditional fuel and can increase the rate of wear on the after treatmentsystem. In that regard, it may be advantageous to vary when aparticulate filter is regenerated to reduce fuel consumption and extendafter treatment system usable life.

Thus, there is a need for one or more metrics for accurately estimatingparticulate loading of particulate filters or soot filters.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

In accordance with aspects of the present disclosure, a system isprovided for determining an amount of NO₂ exiting an oxidation catalystof an exhaust after treatment system. The system includes a spacevelocity generator configured to generate the space velocity of anoxidation catalyst as a function of oxygen concentration present in theexhaust entering the oxidation catalyst, an NO₂ equilibrium generatorconfigured to generate a value indicative of the NO₂ equilibrium of theexhaust, an NO₂ equilibrium fraction generator configured to obtain aNO₂ equilibrium fraction, and an NO₂ exit generator configured togenerate a value indicating the quantity of NO₂ exiting the oxidationcatalyst based on the value indicative of the NO₂ equilibrium of theexhaust and the NO₂ equilibrium fraction.

In accordance with another aspect of the present disclosure, a method isprovided for determining an amount of NO₂ exiting an oxidation catalystof an exhaust after treatment system. The method includes measuring anamount of NO_(x) present in a stream of exhaust prior to introductioninto an oxidation catalyst, determining an amount of NO in the NO_(X),and determining an amount of NO₂ exiting the diesel oxidation catalystas a function of space velocity and temperature. In some embodiments,the determined amount of NO₂ and the space velocity are dependent on thelevel of oxygen present in the NO_(X).

In accordance with another aspect of the present disclosure, a computerimplemented method is provided for determining an amount of NO₂ exitingan oxidation catalyst of an exhaust after treatment system. The methodincludes obtaining a bed temperature of the oxidation catalyst,calculating the space velocity (SV) of the oxidation catalyst,normalizing the space velocity (SV) as a function of oxygenconcentration present in the exhaust, obtaining an NO₂ equilibriumfraction as a function of bed temperature and normalized SV, determiningan NO₂ equilibrium, and calculating an amount of NO₂ exiting theoxidation catalyst based on the NO₂ equilibrium determination and theobtained NO₂ equilibrium fraction.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of one example of an after treatment systemcoupled to an internal combustion engine in accordance with aspects ofthe present disclosure;

FIG. 2 is a schematic view of one example of an internal combustionengine in accordance with aspects of the present disclosure;

FIG. 3 is a schematic diagram of one example of an after treatmentsystem formed in accordance with aspects of the present disclosure, thesystem showing one example of an electronic control unit (ECU);

FIG. 4 is one graphical example of a multi-dimensional look up table(LUT) formed in accordance with aspects of the present disclosure.

FIG. 5 is a block diagram on another example of an electronic controlunit (ECU) formed in accordance with aspects of the present disclosure;and

FIG. 6 is a flow diagram of one example of a method for determining theamount of NO₂ present in the exhaust that exits the oxidation catalystin accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings where like numerals reference like elements is intended as adescription of various embodiments of the disclosed subject matter andis not intended to represent the only embodiments. Each embodimentdescribed in this disclosure is provided merely as an example orillustration and should not be construed as preferred or advantageousover other embodiments. The illustrative examples provided herein arenot intended to be exhaustive or to limit the claimed subject matter tothe precise forms disclosed. Similarly, any steps described herein maybe interchangeable with other steps, or combinations of steps, in orderto achieve the same or substantially similar result.

The following description sets forth one or more examples of exhaustafter treatment systems for internal combustion engine powered vehiclesand methods therefor. In some embodiments, logic in the form of one ormore routines implemented by one or more components of the exhaust aftertreatment systems is disclosed. Examples of such routines set forth oneor more methods for determining the quantity of NO₂ present in theexhaust that exits an oxidation catalyst, such as a diesel oxidationcatalyst (DOC), without the use of an NO₂ sensor. In particular, sinceNO₂ sensors are not presently used on vehicles due to their complexityand expense, methods are needed for determining the amount of NO₂ in theexhaust at various stages of the after treatment system from othermeasurable and/or known operating parameters of the engine/aftertreatment system. The results from the methods described herein may thenbe used to estimate the amount of soot present in the particulatefilter. This estimated value of soot present in the particulate filtercan then be subsequently used to determine when the particulate filtershould be actively regenerated.

As will be described in more detail below, embodiments of the presentdisclosure utilize one or more models that determine the amount of NO₂exiting an oxidation catalyst at a given time. In several embodiments ofthe present disclosure, the amount of NO₂ exiting the oxidation catalystis based on measured or sensed conditions within the system andpredictive calculations of the amount of NO₂ generated by the quantityof NO and O₂ in the exhaust gas in the presence of a catalyst. Furtheras will be described in detail below, embodiments of the modelsdescribed herein include the effects of oxygen on the quantity of NO₂exiting the oxidation catalyst. One goal of the present disclosure,among others, is to simplify the on-board calculations and/or equipmentneeded to determine when to actively regenerate the particulate filter.

Prior to discussing the details of various aspects of the presentdisclosure, it should be understood that one or more sections of thefollowing description may be presented in terms of logic and operationsthat may be performed by conventional electronic components. Theseelectronic components, which may be grouped in a single location ordistributed over a wide area, generally include controllers,microcontrollers, control units, processors, microprocessors, etc. Itwill be appreciated by one skilled in the art that any logic describedherein may be implemented in a variety of configurations, including butnot limited to hardware, software, and combinations thereof. Incircumstances were the components are distributed, the components areaccessible to each other via communication links.

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of exemplary embodiments ofthe present disclosure. It will be apparent to one skilled in the art,however, that many embodiments of the present disclosure may bepracticed without some or all of the specific details. In someinstances, well-known process steps have not been described in detail inorder not to unnecessarily obscure various aspects of the presentdisclosure. Further, it will be appreciated that embodiments of thepresent disclosure may employ any combination of features describedherein.

Referring now to FIG. 1, there is shown a block diagram of severalcomponents of a vehicle powertrain. The components include an internalcombustion engine 20 in flow communication with one or more selectedcomponents of an exhaust after treatment system 24. The internalcombustion engine 20, comprising a plurality of cylinders, one cylinder30 of which is shown in FIG. 2, is controlled by electronic control unit34, sometimes referred to as the engine control unit or ECU. As bestshown in FIG. 2, the internal combustion engine 20 includes a combustionchamber 36 and cylinder walls 40 with a piston 42 positioned therein andconnected to a crankshaft 44. The combustion chamber 36 is showncommunicating with an intake manifold 46 and an exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. In the example of FIG.2, the internal combustion engine 20 is shown as a direct injection,diesel engine with injector 88 located to inject fuel directly intocylinder 30. Fuel is delivered to fuel injector 88 by a fuel system (notshown), including, for example, a fuel tank, fuel pump, and a highpressure common rail system. In one embodiment, the fuel injector 88delivers fuel under control of the ECU 34. Both fuel quantity andinjection timing may be adjustable.

In addition to those signals previously discussed, the ECU 34 alsoreceives various signals from one or more sensors coupled to engine 20,including but not limited to: engine coolant temperature (ECT) fromtemperature sensor 62 coupled to cooling sleeve 64; a measurement ofmanifold pressure (MAP) from pressure sensor 68 coupled to intakemanifold 46; a measurement (AT) of manifold temperature from temperaturesensor 70; an engine speed signal (RPM) from engine speed sensor 72coupled to crankshaft 44. As will be described in more detail below, oneor more of these and other signals may be stored in memory of the ECU 34or other data store.

Referring back to FIG. 1, the engine 20 is coupled to the exhaust gasafter treatment system 24. As known in the art, combustion of fuel ininternal combustion engines produce a number of combustion productsincluding particulates, hydrocarbons (“HC”), carbon monoxide (“CO”),oxides of nitrogen (“NO_(X)”), including NO and NO₂, and oxides ofsulfur (“SO_(X)”). These combustion products are referred to in bothFIGS. 1 and 2 as “exhaust,” which exits the exhaust manifold 48 (FIG.2). In some embodiments, an optional turbocharger (not shown) can becoupled to engine 20 via exhaust manifold 48 and intake manifold 46. Theturbocharger may include a compressor in the intake and a turbine in theexhaust coupled via a shaft.

In the embodiment shown in FIG. 2, the engine 20 may further include anexhaust gas recirculation (EGR) system 76 that recirculates the exhaustvia piping 78 to the intake manifold 46. The EGR system 76 may furtherinclude an EGR control valve 80 that controls the amount of exhaustrecirculation of the engine, and receives control signals from the ECU34. Based on various engine and/or after treatment system operatingcharacteristics, the ECU 34 can control the EGR system 76 in order toprovide, for example, two or more ERG modes of operation. For example, afirst EGR mode can be an EGR “off” mode wherein the control valve 80 isin a closed state, while a second ERG mode can be an ERG “on” modewherein the control valve 80 is an open state. In some embodiments, theEGR control valve 80 can be controlled in order to vary the timing andquantity of exhaust presented to the intake manifold 46. In thatregards, the ERG “on” mode can be separated into more than one mode,including ERG LOW and EGR HIGH. It will be appreciated that when the EGRsystem 76 is turned on, the amount of oxygen present in the exhaustdecreases. In other embodiments, the engine may additionally oralternatively include a throttle 84.

Returning to FIG. 1, the exhaust after treatment system 24 optionallyincludes a catalyst system 96 upstream of a particulate filter 100. Inthe embodiment shown, the catalyst system 96 is a diesel oxidationcatalyst (DOC) 96 coupled in flow communication to receive and treatexhaust from the engine 20. The DOC 96 is preferably a flow throughdevice that includes either a honey-comb like or plate-like substrate.The substrate has a surface area that includes a catalyst. The catalystis typically an oxidation catalyst, which may include a precious metalcatalyst, such as one containing platinum, for rapid conversion ofhydrocarbons (HC), carbon monoxide (CO) and nitric oxide (NO) in theengine exhaust gas. In one embodiment, the honey-comb like or plate-likesubstrate is coated with a platium group metal catalyst.

The oxidation catalyst 96 may also be used to supply heat in the exhaustafter treatment system, wherein an exotherm is created when extra HC isreduced over the oxidation catalyst. This can be accomplished through,for example, in-cylinder injection during either or both of a power orexhaust stroke of the engine (in a direct injection engine) or any of anumber of other alternatives, such as retarding injection timing,increasing EGR and intake throttling. Alternatively, hydrocarbons may beinjected directly into the exhaust gas stream entering the oxidationcatalyst. For example, HC from the fuel tank or from a storage vesselmay be delivered to the exhaust system to generate heat for heating theparticulate filter 100 for active regeneration purposes. As exhaust gasfrom the engine 20 traverses the catalyst, CO, gaseous HC and liquid HC(unburned fuel and oil) are oxidized. As a result, these pollutants areconverted to carbon dioxide and water.

The treated exhaust gases may then proceed to the particulate filter100, such as a diesel particulate filter (DPF) 100. The DPF 100 isutilized to capture unwanted diesel particulate matter from the flow ofexhaust gas exiting engine 20. The diesel particulate matter includessub-micron size particles found in diesel exhaust, including both solidand liquid particles, and may be classified into several fractionsincluding: inorganic carbon (soot), organic fraction (sometimes referredto as SOF or VOF), and sulfate fraction (sometimes referred to ashydrated sulfuric acid). The DPF 100 can be manufactured from a varietyof materials including but not limited to cordierite, silicon carbide,and/or other high temperature oxide ceramics. The DPF 100 also includesat least one catalyst to catalyze the oxidation of trapped particulateand/or exhaust gas components. For example, the catalyst may include abase metal/zeolite formulation with optimum NO_(X) conversionperformance in the range of approximately 200-500 degree C., althoughany known oxidation catalyst may be used.

Once soot accumulation has reached a predetermined level in the DPF 100,active regeneration can be initiated by the ECU 34. As briefly discussedabove, filter regeneration may be accomplished by heating the DPF 100 toa temperature that will burn soot particles at a faster rate than thedeposition of new soot particles, for example, 400-600 degrees C. In oneexample, the DPF 100 can be a catalyzed particulate filter containing awashcoat of precious metal, such as Platinum, to lower the sootcombustion temperature and also to oxidize hydrocarbons and carbonmonoxide to carbon dioxide and water.

The exhaust after treatment system 24 may further include an optionalSelective Catalytic Reduction (SCR) system 104. Reductant, such asaqueous urea, can be stored on-board and injected in the exhaust systemupstream of an SCR catalyst. In one embodiment, the SCR catalystincludes a substrate constructed from various cermanic materials, suchas titanium oxide, which can be coated with one or more active catalyticcomponents, such as one or more oxides of base metals, zeolites, and/orprecious metals.

Turning now to FIG. 3, additional components of the system 24 will nowbe described. As best shown in FIG. 3, the system 24 includes one ormore sensors associated with components of the system 24. In oneembodiment, the one or more sensors may include one or more temperaturesensors 108. As best shown in FIG. 3, at least one temperature sensor108 is associated with the DOC 96 for measuring the temperature of theexhaust gas as it enters the DOC 96. In other embodiments, twotemperature sensors 108 a and 108 b may be used. In such embodiments,one sensor may be located at the entrance or upstream from the DOC 96and another sensor may be located at the exit or downstream from the DOC96. Information from temperature sensor(s) 108 is provided to ECU 34. Analgorithm may then be used by ECU 34 to determine the operatingtemperature of the DOC 96, sometimes referred as the bed temperature ofthe DOC 96.

The one or more sensors also includes an NO_(X) sensor 110 that sensesthe quantity of NO_(X) exiting the engine 20 upstream of DOC 96, andprovides to the ECU 34 a signal indicative of the amount of NO_(X)present in the engine exhaust. Also located upstream of the DOC 96 arethe oxygen sensor 112, the mass flow sensor 114, and a pressure sensor116. For example, an oxygen sensor 112 may be positioned in fluidcommunication with the flow of exhaust gas exiting the engine 20,upstream of the DOC 96. The oxygen sensor 112 is preferably a universalexhaust gas oxygen sensor or lambda sensor, but could be any type ofoxygen sensor. The oxygen sensor 112 is connected with ECU 34 andgenerates electric signals that are indicative of the amount of oxygencontained in the flow of exhaust gas. In other embodiments, the NO_(X)sensor 110 may be of the type that also measures the quantity of oxygencontained in the exhaust gas, such as a NO_(X) sensor currentlyavailable from Bosch.

Similar to the oxygen sensor 112 and/or NO_(X) sensor 110, the mass flowsensor 114 and a pressure sensor 116 may also be positioned in fluidcommunication with the flow of exhaust gas exiting the engine 20,upstream from DOC 96. The mass flow sensor 114 and a pressure sensor 116are connected to the ECU 34 and generate electric signals that areindicative of the mass flow rate and pressure of the exhaust gas.Signals generated by the aforementioned sensors, among others, arestored in memory of the ECU 34 or other data store(s) and may beutilized by one or more NO₂ determination applications, as will bedescribed in more detail below.

Referring now to FIG. 5, there is illustrated a functional block diagramof one example of the ECU 34. It will be appreciated that the ECU 34 canbe implemented in a variety of hardware, software, and combinationhardware/software configurations, for carrying out aspects of thepresent disclosure. It will be appreciated that the functions carriedout by the ECU 34 related to the after treatment of exhaust may bealternatively carried out by a discrete controller associated with theafter treatment system 24 or integrated or associated with another oneor more controllers of the vehicle, such as the engine control module,among others.

In the embodiment shown in FIG. 5, the ECU 34 may include but is notlimited to an nSV generator 144, an NO₂ EQ generator 146, an NO2 EQFraction generator 148, and an NO2 Exit generator 150. The ECU 34 mayreceive data from one or more data stores 154. In one embodiment, theone or more data stores 154 may include a NO₂ fraction LUT 158, arewriteable memory section 160, and data 162, such as the exhaust gasconstant (R), NO₂ equilibrium constant, K(t), the volume of the DOC 96,etc. In some embodiments, the LUT 158 is a multi-variable LUT, and maybe generated from empirically derived data as a function of nSV and DOCbed temperature. Accordingly, with known nSV and DOC bed temperaturevalues, the LUT 158 is capable of outputting a value representing an NO₂equilibrium fraction. The NO2 equilibrium fraction represents theamount, as a fraction or a percentage (less than one) of the reaction ofNO and O₂ that has moved to equilibrium (resulting in NO₂). Onegraphical example of the LUT 158 is shown in FIG. 4. To ease thecalculations made by the ECU 34, the one or more data stores 154 in someembodiments may also include LUTs 164 and 166 that include data in theform of the square root of the NO₂ equilibrium constant, K(t), as afunction of bed temperature of the DOC 96, and the square root of the O₂fraction, respectively.

Still referring to FIG. 5, the nSV generator 144 determines the spacevelocity of the engine exhaust through the DOC 96 as a function ofexhaust oxygen, referred to herein as nSV. Standard space velocity (SV)is equal to the volume of exhaust flow per volume of the DOC 96. Assuch, nSV can be determined with data from one or more sensors 108, 112,114, 116, including mass flow rate and pressure of the exhaust, the bedtemperature of the DOC 96, and the percentage of oxygen present in theexhaust, in addition to data stored in memory section 160, including thegas constant (R) of the exhaust, the volume of the DOC 96, and/or thelike.

In one embodiment, the space velocity (SV) may be calculated from thefollowing equation.

SV=Volume_(exhaust)/Volume_(catalyst); where

Volume_(exhaust)=Mass Flow Rate_(exhaust)/DensitY_(exhaust); and

DensitY_(exhaust)=Pressure_(exhaust)/R_(exhaust)×Temperature_(exhaust)  (1)

In one embodiment, nSV may be calculated from the results of equation(1) above with the following equation.

nSV=SV/O_(2exhaust)  (2)

The NO₂ EQ generator 146 determines the amount of NO₂ that would bepresent in the exhaust exiting the DOC if equilibrium conditions werepresent. In some embodiments, NO₂ equilibrium can be calculated withdata from one or more sensors 108, 110, 112, including the DOC bedtemperature, the percentage of oxygen present in the exhaust, and thequantity (in ppm) of NO_(X) of the exhaust, in addition to data storedin memory section 160, including the nitrogen dioxide equilibriumconstant, K(t), and/or the like.

In one embodiment, the amount of NO₂ at equilibrium can be calculated bythe following equation.

K(t)=[NO₂]²/[NO]²[O₂], where NO_(X)=NO₂+NO;  (3)

Solving for NO₂ and substituting (NO_(X)−NO₂) for NO results in equation(4).

NO₂=[NO_(X)][O₂]^(1/2) [K(t)]^(1/2)/[1+[O₂]^(1/2) [K(t)]^(1/2)]  (4)

For ease of calculation, in one embodiment the square root of theequilibrium constant, K(t), may be obtained from a LUT 164 stored indata store 154. Likewise, in one embodiment the square root of the O₂percentage may be obtained from the LUT 166 stored in date store 154.Other embodiments may include configurations of hardware and/or softwarefor easily computing NO₂ from equation (4), as described in more detailbelow.

With the results of the nSV generator 144 and DOC temperature fromsensor 108, the NO2 EQ fraction generator 148 outputs the NO₂equilibrium fraction with the use of the LUT 158. Next, with the outputsof both the NO₂ EQ fraction generator 148 and the NO₂ EQ generator 146,the NO₂ exit generator 150 determines the quantity of NO₂ (ppm) in theexhaust that exits the DOC, referred to herein as NO₂ EXIT.

In one embodiment, NO₂ EXIT may be calculated with the followingequation.

NO₂ EXIT=NO₂ equilibrium×NO₂ equilibrium fraction  (5)

FIG. 3 depicts another embodiment of the ECU, generally designated 234,in accordance with aspects of the present disclosure. As shown in FIG.3, the ECU 234 is depicted as a computing device that includes aprocessor 220, a memory 222, and I/O circuitry 224 suitablyinterconnected via one or more buses. In this regard, the processor 220is configured to execute instructions and to carry out operationsdefined in one or more applications 226 or program modules that residein the memory 222. The memory 222 depicted in FIG. 3 is one example ofcomputer-readable media suited to store data, such as sensor data andprogram data in the form of one or more look up tables (LUTs), andprogram modules that implement aspects of the disclosed subject matter.The ECU 234 is connected in communication with one or more sensors, suchas sensors 108-116, etc., and other data sources via the I/O circuitry224.

By way of example, and not limitation, computer readable media includesvolatile and non-volatile and removable and non-removable memory,implemented in any method or technology capable of storing information,such as computer-readable instructions, data structures, programmodules, or other data. By way of example, computer readable mediainclude, but are not limited to, RAM, ROM, EPROM, EEPROM, flash memory,CD-ROM, digital versatile disks (DVD), etc., or any other medium thatcan be used to store information for access by the processor 220.

The memory 222 may include program modules, applications, and the likethat include algorithms or routines configured to perform operationsthat are executable by the processor 220. In that regard, the memory 222includes an NO₂ determination application for determining the amount ofNO₂ present in the exhaust gas exiting the DOC 96, referred to herein asNO₂ Exit. Additionally, the memory 222 may include single ormulti-dimensional performance maps or look-up tables (LUTs) that areaccessed by the processor 220. One such LUT includes a NO₂ EQ fractionLUT 258 described above with reference to FIG. 5. The LUT 258 is amulti-variable LUT, and is generated from empirically derived data as afunction of nSV and DOC bed temperature. Accordingly, with known nSV andDOC bed temperature values, the LUT 258 is capable of outputting a valuerepresenting an NO₂ equilibrium fraction. The NO2 equilibrium fractionrepresents the amount, as a fraction or a percentage (less than one) ofthe reaction of NO and O₂ that moved to equilibrium (resulting in NO₂).The memory 222 in other embodiments may also include LUTs 264 and 266that include data in the form of the square root of the equilibriumconstant, K(t), for the formation of NO₂ as a function of bedtemperature of the DOC 96, and the square root of the O₂ fraction,respectively.

The NO₂ determination application includes instructions that whenexecuted by the processor 220 performs one or more functions, includingone or more NO₂ estimation routines, as will be described in more detailbelow. In one embodiment, the NO₂ determination application is capableof polling for or receiving data from one or more system components,analyzing the data received from the system components, and/orgenerating control signals to be transmitted to the components of thesystem 24, such as starting active regeneration of the DPF via the fuelcontrol device 80 or the like. The NO₂ determination application furtherretrieves stored data including data from one or more LUTs, includingLUT 258.

During operation of the vehicle, the NO₂ determination application isprogrammed to obtain and/or calculate the space velocity of the engineexhaust through the DOC 96 as a function of exhaust oxygen, referred toherein as nSV. In some embodiments, nSV can be calculated with data,including the mass flow rate and pressure of the exhaust, the bedtemperature of the DOC, and the oxygen percentage of the exhaust, datastored in memory 222, including the gas constant (R) of the exhaust andthe volume of the DOC, or the like. The NO₂ determination applicationmay be further configured to cause the processor 120 to access the LUT258 in memory 222 in order to obtain the NO₂ equilibrium fraction as afunction of DOC bed temperature and the nSV calculation. The NO₂equilibrium fraction indicates how far, as a fraction or percentage, thereaction of NO and O₂ has moved towards equilibrium (resulting in NO₂).The NO₂ determination application may further cause the processor 120 totake the results of the LUT 258, i.e., the NO₂ equilibrium fractionbased on the DOC bed temperature and calculated nSV, and determine, NO₂EXIT, the amount of NO₂ present in the exhaust exiting the DOC 96. Thiscalculation may occur after application 230 causes the processor 220 tocalculate the amount of NO₂ that would be present if equilibriumconditions were present, referred to as NO₂ equilibrium. In a fewembodiments, NO₂ EXIT is the product of the NO₂ equilibrium fraction andNO₂ equilibrium.

It will be appreciated that in some embodiments, NO₂ equilibrium can becalculated according to equation (4) above with data from one or moresensors, including the DOC bed temperature, the oxygen percentage of theexhaust, and the quantity (in ppm) of NO_(X) of the exhaust, data storedin memory 222, including the NO₂ equilibrium constant, K(t), and/or thelike.

One or more routines that can be implemented within the environmentdescribed above, including engine 20 and/or exhaust after treatmentsystem 24, will now be described. As will be appreciated by one skilledin the art, the specific routines described below in the flowcharts mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various acts or functions illustrated may be performed inthe sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages, but is provided for ease of illustrationand description. Although not explicitly illustrated, one or more of theillustrated acts or functions may be repeatedly performed depending onthe particular strategy being used.

Referring now to FIG. 6, one example of a method 600 is set forth fordetermining NO₂ EXIT, or the amount of NO₂ present in the exhaust gasthat exits the DOC 96. The method 600 may be implemented by one or morecomponents, including ECUs 34, 234, etc. described above. With theresults of such determination, timing and/or length of activeparticulate filter regeneration of the DPF can be controlled.

The method begins at block 602 and proceeds to block 606, where spacevelocity (SV) of the catalyst, DOC 96, is calculated. Next, at block610, the space velocity calculation is normalized as a function ofoxygen concentration present in the exhaust, resulting in normalizedspace velocity (nSV). From block 610, the method proceeds to block 614,where an NO₂ equilibrium fraction is obtained as a function of DOC bedtemperature and normalized SV (nSV). In one embodiment, the NO₂equilibrium fraction is obtained from a LUT, such as LUT 158, 258. Next,NO₂ equilibrium is calculated is block 620. The method then proceeds toblock 624, where the amount of NO₂ EXIT is calculated from the resultsof the NO₂ equilibrium calculation and the obtained NO₂ equilibriumfraction. The method ends at block 628.

The principles, representative embodiments, and modes of operation ofthe present disclosure have been described in the foregoing description.However, aspects of the present disclosure which are intended to beprotected are not to be construed as limited to the particularembodiments disclosed. Further, the embodiments described herein are tobe regarded as illustrative rather than restrictive. It will beappreciated that variations and changes may be made by others, andequivalents employed, without departing from the spirit of the presentdisclosure. Accordingly, it is expressly intended that all suchvariations, changes, and equivalents fall within the spirit and scope ofthe present disclosure.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A system for determiningan amount of NO₂ exiting an oxidation catalyst of an exhaust aftertreatment system, comprising: a space velocity generator configured togenerate the space velocity of an oxidation catalyst as a function ofoxygen concentration present in the exhaust entering the oxidationcatalyst; an NO₂ equilibrium generator configured to generate a valueindicative of the NO₂ equilibrium of the exhaust; an NO₂ equilibriumfraction generator configured to obtain a NO₂ equilibrium fraction; andan NO₂ exit generator configured to generate a value indicating thequantity of NO₂ exiting the oxidation catalyst based on the valueindicative of the NO₂ equilibrium of the exhaust and the NO₂ equilibriumfraction.
 2. The system of claim 1, wherein the space velocity generatoris configured to calculate the space velocity of the oxidation catalystas a function of the volume of the oxidation catalyst and the exhaustflow through the oxidation catalyst.
 3. The system of claim 1, whereinthe NO₂ equilibrium generator is configured to generate the valueindicative of the NO₂ equilibrium of the exhaust based on one or more ofoxidation catalyst temperature, gas constant (K) of NO₂, the oxygenconcentration, and quantity of NO_(X).
 4. The system of claim 1, whereinthe NO₂ equilibrium fraction generator is configured to obtain the NO₂equilibrium fraction based on oxidation catalyst temperature and thespace velocity.
 5. A method of determining an amount of NO₂ exiting anoxidation catalyst of an exhaust after treatment system, the methodcomprising: measuring an amount of NO_(x) present in a stream of exhaustprior to introduction into an oxidation catalyst; determining an amountof NO in the NO_(X); determining an amount of NO₂ exiting the dieseloxidation catalyst as a function of space velocity and temperature,wherein the determined amount of NO₂ and the space velocity aredependent on the level of oxygen present in the NO_(X).
 6. The method ofclaim 5, wherein the amount of NO₂ exiting the oxidation catalyst can beused to estimate the amount of particulate being passively removed froma diesel particulate filter.
 7. The method of claim 5, wherein theamount of NO is determined without the use of the NO sensor.
 8. Acomputer implemented method for determining an amount of NO₂ exiting anoxidation catalyst of an exhaust after treatment system, the methodcomprising, comprising: obtaining a bed temperature of the oxidationcatalyst; calculating the space velocity (SV) of the oxidation catalyst;normalizing the space velocity (SV) as a function of oxygenconcentration present in the exhaust; obtaining an NO₂ equilibriumfraction as a function of bed temperature and normalized SV; determiningan NO₂ equilibrium; and calculating an amount of NO₂ exiting theoxidation catalyst based on the NO₂ equilibrium determination and theobtained NO₂ equilibrium fraction.
 9. The method of claim 8, wherein theNO₂ equilibrium fraction is obtained from a look-up table.
 10. Themethod of claim 8, wherein the oxidation catalyst is a diesel oxidationcatalyst.